Transcript EtherNet/IP Switch Features

Ethernet Switch Features
Important to EtherNet/IP
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Switch Features are Important
The proper selection of switches to be used in real-time (I/O) EtherNet/IP networks is
critical. There are several features that are very important and can provide the
appropriate infrastructure for your application. The following features need to be
considered:
Required:
• Full-duplex capability on all ports
• IGMP Snooping
• Port Mirroring
Recommended:
• VLAN
• Auto-negotiation and manually configurable speed/duplex
• Wire-speed switching fabric
• SNMP for switch management
• IEEE 802.1D Spanning Tree Protocol
Desirable: see last slide
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Full-duplex
Full-duplex capability on all ports:
Full duplex capability eliminates collisions on the wire due to the
separate transmit and receive channels for each device. Combined
with the speed of switches available today, delays related to
collisions or traffic in the switch can be made negligible. The end
result is you can achieve a high degree of determinism with an
EtherNet/IP network and it works well for I/O control.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Internet Group Multicast Protocol (IGMP)
Snooping
IGMP Snooping:
Sends out IGMP polls
to determine who is in
a multicast group
to plant network
IGMP snooping constrains the
flooding of multicast traffic by
dynamically configuring switch
ports so that multicast traffic is
forwarded only to ports associated
with a particular IP multicast group.
Layer 3 Switch or Router
Layer 2 Switch
Switches that support IGMP
snooping “learn” which ports have
devices that are part of a particular
multicast group and only forward
the multicast packets to the ports
that are part of the multicast group.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Listens to the polls
and responses to
determine who is in
each multicast group
Layer 2 Switch
Controller
(Consumer)
I/O
(Multicast
Producer)
IGMP Snooping - continued
IGMP Snooping:
Normally, a commercial layer 2
switch that “supports” IGMP
snooping needs a router (which
could be a layer 3 switch) to
send out the IGMP polls in order
to learn what devices are part of
the multicast group.
to plant network
Note that none of
the multicast traffic
hits the router
Layer 3 Switch or Router
Layer 2 Switch
*** IMPORTANT ***
Some industrial layer 2 switches
support IGMP snooping without
the requirement for a router or
layer 3 switch to be present to
send out the IGMP polls.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Layer 2 Switch
Controller
(Consumer)
I/O
(Multicast
Producer)
Port Mirroring
Port Mirroring:
Port mirroring refers to the ability to direct a duplicate of the frames
being transmitted on one port to another port. This allows a traffic
analyzer to be connected to a switch and have the ability to monitor
the traffic on a given port. Without port mirroring, an analyzer is not
able to see frames on other ports.
Traffic analyzers are used extensively by people who support
Ethernet networks. Therefore, it is critical that a switch is selected
that supports port mirroring so that a traffic analyzer will function
correctly on the network.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Virtual Local Area Networks (VLANs)
VLAN:
The benefits of VLANs are that a switch can be configured to handle two isolated networks
without the traffic from one network burdening the other. IP multicast traffic from VLAN 1 will
not reach VLAN 2. For multicast traffic, you could accomplish the same thing with IGMP
snooping. However, a VLAN will also block unicast and broadcast traffic, and adds a
measure of security between networks.
PC
Controller1
1
Controller2
2
3
Switch
VLAN 1
4
I/O
5
I/O
VLAN 2
6
7
I/O
8
I/O
I/O
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Auto-negotiation / Manually Configurable
Speed/Duplex
Auto-negotiation and manually configurable speed/duplex:
Auto-negotiation allows devices to select the most optimal way to
communicate without the user having to configure the devices. If a
manually configured device is attached to an auto-negotiation device
there can be problems which result in a high rate of CRC errors. While all
100 Mbps devices are required to support auto-negotiation, most existing
10 Mbps devices do not.
Two other areas where this switch feature can be helpful include when
fibers converters are used in a system (auto-negotiation is not supported
by fiber links) and to eliminate potential incompatibilities in the
implementation of the auto-negotiation by different device vendors.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Wire-speed Switching Fabic
Wire-speed switching fabric:
The switch fabric capacity is a measure of the maximum traffic that a
switch can handle without dropping a packet. Wire speed switching
fabric refers to a switch that can handle the maximum data rate of
the network on each of its ports.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Simple Network Management Protocol
(SNMP)
SNMP:
SNMP, Simple Network Management Protocol, is a TCP/IP protocol
used to obtain statistical information about a device. SNMP software
is very popular with network managers. It allows a network
manager to view and modify a wide variety of network parameters,
and also provides a common way to manage many diverse vendor
products utilizing a single Network Management Tool.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
IEEE 802.1D Spanning Tree Protocol
IEEE 802.1D Spanning Tree Protocol:
Ethernet infrastructures can be designed to provide redundant
backbone connections for improved fault tolerances. The Spanning
Tree Protocol is to ensure that although multiple paths may exist
between two devices connected to the infrastructure, only a single
path will be used for communications at any one time.
The switch should have the ability to enable and disable this feature
on a per port basis.
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.
Desirable Switch Features
• IEEE 802.1p Frame Prioritization
• IP address blocking
– Restricts traffic to IP Addresses in specific range (down to one)
•
•
•
•
•
•
DHCP Option 82
Limited DHCP Server (for small systems)
Auto-restore of switch config on replacement
Per port broadcast and multicast storm control
Port Trunking for applications with many switches
Various security functions
Copyright © 2005 Rockwell Automation, Inc. All rights reserved.